Future generation aircraft (including helicopters) now in planning and/or development phases (as well as many present generation aircraft) are complex systems comprised of a large number of interrelated, complex subsystems such as the airframe, powerplant, flight controls, avionics, navigation equipment, armament, etc. Such subsystems generate significant amounts of status data, much of which must be frequently monitored by the pilot for the safe and/or efficient operation and/or pilotage of the aircraft. A considerable portion of pilot workload in these future generation aircraft will be devoted to monitoring the status of the aircraft subsystems during flight operations via reference to the generated status data.
In addition, mission requirements for such future generation aircraft may involve a greater percentage of high pilot workload flight operations such as nap-of-the-earth (NOE), adverse weather, and/or night flying. Such high pilot workload flight operations require the pilot to maintain a continual spatial awareness of aircraft orientation and/or location with respect to the external world and a situational awareness of objects of interest in the external world vis-a-vis the aircraft in addition to continual monitoring of the status of aircraft subsystems.
It will be appreciated that the task of monitoring the status of the various aircraft subsystems may conflict with the tasks of maintaining continual spatial and situational awareness of the external world. To monitor the status of aircraft subsystems, the pilot may have to divert his attention from the observation of the external world outside the cockpit to reference generated status data. Such diversions may lead to losses, in varying degrees, of spatial and/or situational awareness of the external world, which, in turn, may lead to less than optimal flight conditions, especially during high pilot workload flight operations.
Current aircraft design methodology strives to optimize the interrelationship between the functional task of monitoring aircraft status information and the functional tasks of maintaining continual spatial and situational awareness of the external world vis-a-vis the aircraft. Such design methodology seeks systems and methods that allow vital aircraft status information to be accessible to the pilot in such a manner that there is no interference with the continual spatial and situational awareness functions being performed by the pilot. In addition, such aircraft status information should be presented in a manner consonant with the spatial orientation and perspective of the pilot to preclude any decoupling among the various functional tasks. Such decoupling may lead to increased pilot workload (to maintain a viable frame of reference) and/or to pilot disorientation.
Electro-optical systems have been developed to provide aircraft status information to the pilot to facilitate simultaneous accomplishment of both the status monitoring functions and the spatial and situational awareness functions. These systems generate symbolic and digital status information images that correspond to the aircraft status information generated by the various aircraft subsystems and superimpose such symbolic status information images into the pilot's field of vision. The images are typically introduced into the pilot's field of vision by means of collimated light rays so that the symbolic images appear to be at optical infinity with respect to the pilot's visual system.
Thus, the pilot views the external world outside of the cockpit at infinity and simultaneously sees symbolic and digital images at infinity. The superimposition of two sets of images, i.e., the external world and electronically generated symbolic and digital status information images, enable the pilot to simultaneously maintain awareness of the status of the aircraft, the spatial orientation of the aircraft with respect to the external world, and a situational awareness of the external world vis-a-vis the aircraft.
Exemplary prior art electro-optical systems utilizing collimated light rays to generate symbolic images include head-up display (HUD) subsystems and helmet mounted display (HMD) subsystems. Representative examples of HUD and HMD subsystems are illustrated in U.S. Pat. Nos. 4,446,480, 4,439,775, 4,439,157, 4,305,057, 4,269,476, and 3,923,370. While such electro-optical systems have contributed significantly to the optimization of the interrelationship between the functional task of monitoring aircraft status information and the functional tasks of maintaining continual spatial and situational awareness of the external world vis-a-vis the aircraft during both visual and non-visual flight conditions, it will be appreciated that the significant amounts of aircraft status information required by the pilot for the safe and/or efficient operation and/or pilotage of the helicopter give rise to a number of special problems vis-a-vis the display mechanics of such status information utilizing electro-optical display systems.
Aircraft status is continuously being monitored by a variety of sensors that are interfaced with various helicopter subsystems such as the airframe, powerplant, flight controls, avionics, navigation equipment, armament, etc. and which are operative to provide continuous streams of raw data regarding the status of such subsystems. In addition, other sensors monitor and provide streams of raw data regarding the status of the external world. Such raw data is continuously being analyzed and/or processed by various automated flight systems such as Flight Management Systems, Flight Directors, Autopilots, Stability Augmentation Systems, and Electronic Engine Control Systems which are operative to provide continuous streams of both raw and processed (either combined raw data or derived data based upon raw data) data representative of aircraft status information.
The initial problem encountered in designing an optimized information display system is data selection. That is, a determinative process must be undertaken to prioritize the raw and/or processed data on the basis of information required by the pilot for safe and/or efficient operation and/or pilotage of the aircraft in view of particular flight conditions and mission requirements. Such prioritization must take into account the "channel capacity" of the pilot, i.e., the upper limit as to the amount of information the pilot can effectively visually receive and process.
Once an initial prioritization has been made as to the raw and/or processed data that must be made available to the pilot through an electro-optical display system, the next problem is the optimization of visual coding of information (stimuli) that is presented via the display system. A variety of factors influence visual stimuli coding.
One factor is the number of visual stimuli to be presented versus the amount of display field available. Another factor is the organization of such stimuli vis-a-vis the display field. High priority stimuli should be centrally displayed on the display field while lower priority stimuli may be displayed nearer the edges of the display field. Stimuli discriminability, i.e., the perceivability of the stimuli by the pilot's visual system, must be considered as well as stimuli compatibility, i.e., the naturalness of the stimuli with respect to response expected from the pilot. Another factor to be considered is whether the stimuli represents dichotomous or non-dichotomous status information, i.e., representative of abnormal or normal conditions, respectively, and whether such status information should be available continuously, or, in the case of dichotomous information, when such status information reaches a threshold level wherein safe aircraft operation is affected. Still another factor is whether the stimuli is static or dynamic, and if dynamic, the frequency update interval.
Another important factor to consider is the nature of the stimuli utilized to convey status information, i.e., numerical, alphabetical, alphanumeric, and/or symbolic. Numerical, alphabetical, and alphanumeric stimuli are generally more advantageous for the visual presentation of quantitative and/or language status information. Symbolic stimuli (symbols), on the other hand, are generally more advantageously utilized where relative discriminations based upon quantitative status information are required. Symbols may be presented in one or more dimensions, and such dimensions may be discrete, continuous, and/or interrelated (combined), depending upon the nature of the status information discriminations required with respect thereto.
There exists a continuing need to re-evaluate and/or optimize the format of the status information symbology that is made available to the pilot via the display field of an electro-optical display system regarding aircraft status so that the status information symbology displayed to the pilot provides aircraft status information in a format that is optimized for absolute and relative informational content and perceptability.